only build demos using extras if BUILD_EXTRAS is on


git-svn-id: http://bullet.googlecode.com/svn@2713 08e121b0-ae19-0410-a57b-3be3395fd4fd
fix 'unused' warning. Fixes Issue 770

git-svn-id: http://bullet.googlecode.com/svn@2714 08e121b0-ae19-0410-a57b-3be3395fd4fd
Avoid crash in btCompoundCompoundCollisionAlgorithm if there is no tree for one of the btCompoundShapes
Update the revision, to avoid clearing the child cache each frame


git-svn-id: http://bullet.googlecode.com/svn@2715 08e121b0-ae19-0410-a57b-3be3395fd4fd